Shinozaki Himenos Love Qa Manga :

Shinozaki Himeno has no intention of dating anyone before she's ready to consider marriage; as such, the last year of high school is too early to her. However, she is confessed to by Maruyama, a weirdo who asked her out solely because a friend told him he should try out love. Moreover, he asked to date her for only one month. Since he'll ask someone else if she rejects, Himeno begrudgingly accepts, beginning an unusual relationship.